Some internal combustion engines use a liquefied gas fuel. Such liquefied gas fuel is bottled in a fuel tank, and is vaporized by a vaporizer before it is supplied to the engine. Since the boiling point of liquefied gas fuel is very low, it is readily evaporated. Evaporation of liquefied gas in the fuel tank increases the pressure within the tank. Therefore, the pressure within the tank tends to exceed the pressure the fuel tank can withstand. In such a ease, the evaporated fuel in the fuel tank is transferred to an occlusion tank. If the pressure within the occlusion tank tends to exceed the pressure the occlusion tank can withstands, the evaporated fuel may sometimes released into atmosphere.
If the liquefied gas internal combustion engine of a ear is not operated for a long time, the amount of gas resulting from the evaporation of the liquefied fuel may increase, which may result in release of a larger amount of evaporated fuel into atmosphere.
Japanese Unexamined Patent Publication (KOKAI) No. HEI 4-325757 proposes a system in which occlusion tanks are installed at predetermined sites, and ears are parked at the occlusion tanks, where evaporated fuel in fuel tanks of the ears are transferred to the occlusion tanks. The gas occluded in the occlusion tanks may be supplied to, for example, home-use gas appliances to thereby efficiently utilize evaporated fuel.
The system disclosed in the Japanese publication, however, requires piping for transferring the evaporated fuel in the fuel tank to the occlusion tank. Furthermore, such piping must be connected to a car to transfer the evaporated fuel from the car fuel tank to the occlusion tank, and, then, disconnected from the car when the car is driven to run, which is very troublesome. If the car cannot be parked at occlusion tank sites, evaporated fuel must be released into atmosphere, which inevitably causes air pollution.
Now, the present invention is described hereinafter. Throughout the specification, a term "evaporated (gas) fuel" or the like is used to denote naturally evaporated gas fuel, such as fuel evaporated in a fuel tank, whereas a term "vaporized fuel" is used to denote gas fuel positively vaporized in a vaporizer for supply to an internal combustion engine.